1. Field of the Invention
The present invention relates generally to methods and devices to monitor patient blood oxygen saturation, and more specifically to methods and devices used to measure the oxygen saturation level of the arterial blood flow of a fetus.
2. Description of the Prior Art
The later stages of pregnancy, as well as labor and delivery, can be a dangerous time for the fetus. If the fetal umbilical cord becomes twisted in an unfavorable position, the placenta detaches prematurely, or if the fetus is otherwise placed in a situation of undue stress, fetal blood oxygen saturation levels can fall dangerously low, resulting in potential fetal brain damage (such as cerebral palsy) or death.
Although fetal heart monitors can be used as a surrogate means to attempt to measure fetal blood oxygen saturation levels, this method is indirect, and thus does not give a fully complete understanding of the fetal status. As a result of this lack of full understanding, emergency medical decisions, such as when to start an emergency caesarean section (C-section) must be made with incomplete knowledge. As a practical matter, doctors tend to err on the side of caution, resulting in many unnecessary C-sections, and the attendant high medical expenses and maternal post-childbirth complications.
Previous attempts to provide this missing fetal blood oxygen saturation levels include the OxiFirst system, produced by Mallinckrodt/Nellcor, now part of Tyco Healthcare. This system, which obtained FDA approval in 2000, works by directly placing the tip of a pulse oximeter sensor up the maternal birth canal, through the cervix, into the uterus and onto the cheek or temple of the fetus. Due to this very invasive insertion process, the method is indicated only after the amniotic membrane has ruptured. This method is described in Levinson et. al., U.S. Pat. No. 5,813,980, and other patents. Unfortunately, due to the high invasiveness and bother of the procedure, the method met with limited medical acceptance in the field, and the manufacturer eventually decided to stop selling the device.
Physicians are highly aware that they will be vulnerable to malpractice lawsuits in the event of potentially preventable fetal neurological damage or death. As a result, armed only with a partial picture of the true physiological status of the fetus, they act very conservatively, and usually elect to do C-sections in the event of any sign of fetal heartbeat issues, even though in most situations, the fetal oxygen levels are still adequate. The problem is now so severe that over 30% of all births are now done by C-section, up from only a few percent only a few decades ago. C-sections cost almost twice as much as vaginal deliveries (now averaging more than $5,000 to $10,000 extra per birth), and there are over four million births per year in the US alone. As a result, each year, many billions of dollars of scarce medical resources are wasted performing unnecessary C-sections that might be better spent saving lives elsewhere.
Thus improved methods for monitoring fetal blood oxygen saturation levels are of high practical utility to the fetus, to the mother, and to society at large.